SANTA CLARA, Calif. — The San Francisco 49ers may be down another running back. After losing backup Matt Breida in the preseason opener due to a separated shoulder, presumptive starter Jerick McKinnon exited Sunday’s practice early with an injured right knee.

The 49ers expect Breida to miss the rest of the preseason, but be healthy enough to be active for the regular season opener at Minnesota in September. McKinnon, looked to be a different story. After being examined by the team’s medical staff on the side of the field after he came up hobbled during team drills, San Francisco announced after practice that McKinnon underwent an MRI on the injured knee. According to ESPN’s Adam Schefter, it revealed only a “muscle strain.”

Up until the injury, McKinnon was in the midst of a strong practice. Breaking several long runs up the sidelines of the practice field, the former Minnesota Viking looked to be focussing on his running game — as opposed to his ability to catch the ball out of the backfield — after netting -4 yards Thursday night against the Dallas Cowboys in a 24-21 win.

After signing a four-year, $30 million contract in the offseason, McKinnon has been expected to take the reigns as San Francisco’s premiere back in 2018 by replacing back Carlos Hyde, who joined the Cleveland Browns in March.

In the wake of Breida’s, and now McKinnon’s injuries, the door looks to be open for the rest of San Francisco’s running back corps. As a result, Joe Williams, Raheem Mostert and Jeremy McNichols will all see an increased number of snaps this week.

Williams had a pedestrian performance Thursday with 27 yards on 11 carries and a touchdown. Mostert put forth a better effort with 57 yards on eight carries while McNichols had 15 yards and scored the second rushing touchdown of the night.

The 49ers have not released a timetable for McKinnon’s return, but considering that he only sustained a muscle strain, it’s possible that he could be back by Week 1, along with Breida.

Monday will be the team’s last practice in Santa Clara before they leave for Houston in the afternoon. The 49ers will likely give an official update on McKinnon at that time.

Notebook:

– Cornerback Richard Sherman made his return to practice Sunday, participating in individual and position drills. Although he was absent for 11-on-11s, Sherman seemed to be moving well. Sherman had spent the last week recovering from a pulled hamstring. According to defensive coordinator Robert Saleh, Sherman will travel with the team to Houston but the 49ers expect to continue to ease him back into game-like conditions.

– Jimmy Garoppolo had an up-and-down practice as he threw two touchdowns but also an interception. The two touchdowns were thrown to receivers Trent Taylor and Kendrick Bourne in a red zone and move-the-ball drill, respectively. The pick was thrown to Adrian Colbert, who is continuing to have a strong camp. Garoppolo is coming off of a three-for-six performance on Thursday in which he saw only one series.